This invention generally relates to sootblowers and particularly relates to improvements in the frame structure and drive mechanism of a retractable sootblower.
Sootblowers are used to project a stream of blowing medium, such as water, air or steam, against heat transfer surfaces within large scale boilers or other heat exchangers to cause slag and ash encrustations to be removed. The impact of the blowing medium produces mechanical and thermal shock which causes the adhering encrustation layers to be removed.
One general category of sootblowers is known as the long retracting type. These devices have a retractable lance tube which is periodically advanced into and withdrawn from the boiler and which is simultaneously rotated such that one or more nozzles at the end of the lance tube project jets of blowing medium against the encrusted heat exchange surfaces in the boiler.
Sootblower designers are constantly striving to enhance design efficiency in terms of construction cost, operation, inventory cost and maintenance. In a conventional retractable sootblower, an elongated frame or beam houses a moveable carriage. The carriage drives a lance tube from one end of the frame to the other during the extension and retraction motion. Various configurations for sootblower frames are known.
In one well-known configuration, sheet metal plate stock is press brake formed to define three sides of a generally rectangular shaped member defining the elongated frame. In a typical installation, the open portion of the frame faces downward. The carriage is driven to move within the frame and the frame supports the lance tube suspended therein. Such conventional sootblower frames are known as closed frames since their upper surface is enclosed and inaccessible. Examples of presently known sootblower designs are provided with reference to U.S. Pat. Nos. 2,668,978; 3,439,376; 3,585,673; 3,604,050, 4,229,854 and 4,351,082. Although these closed frame type sootblowers perform in a satisfactory manner, they do have certain drawbacks.
One drawback results from the method in which the frame is formed. Since the three sided frame member is brake formed from flat sheet metal stock, a limitation on the length (typically twenty feet) of the member is presented by the brake forming machine. To form a longer frame member, separate three sided members are butt welded together. Obviously, forming the butt welds requires an additional and separate bonding step to be included in the production operation. Additionally, the presence of the weld is a site for corrosion development.
In certain sootblower applications, it is difficult to service the various mechanisms of the unit through the open bottom portion of the above mentioned closed frame. In these applications, a frame having an open upper portion which would allow the carriage, feed tube and lance tube and rack to be removed by withdrawing them up through the top portion of the sootblower frame would be more desirable. Although such open top sootblowers can be produced, when using conventional constructions, specifically designed units would have to be produced for specific installations.
In accordance with this invention a sootblower is provide having a frame which features an open construction enabling the sootblower components to be serviced or withdrawn through the bottom of the unit or through the top of the unit.
Another object of this invention is to provide a frame for a sootblower which can be constructed to any desired length while using a common inventory stock for all lengths. It is also an object to provide a sootblower frame in which the side panel are seamless and formed of a unitary construction.
Still another object of the invention is to provide a sootblower frame which is resistant corrosion and which is easily inspected for corrosion damage.
The various boiler configurations require retractable sootblowers of varying lengths. Such lengths range from only several feet long to ones well in excess of 60 feet. With conventional sootblower designs, the vast difference in size requirements has restricted the availability of common construction components thus increasing a manufacturer's inventory requirements and adversely affecting component costs.
The commonality of components becomes difficult since significantly different loads act on the frame structure as a function of the length of the sootblower lance tube. For example, as the extended length of the lance tube increases, the loads applied to the frame increase. In addition, significant loads, from both gravity and fluid reaction forces, act on the sootblower lance tube as it is performing its cleaning function. These loads are transferred to the sootblower carriage which is restrained by the frame.
Various designs for an open-type sootblower frame have been proposed. However, such devices are typically costly to manufacture and do not offer a high degree of accessibility since they are generally constructed to provide either top access or bottom access, but not both. Additionally, in an effort to achieve the necessary structural rigidity, closed box sections or tubes have been proposed which are welded to side panels to form ribs bridging the side panels. These closed tubes have also been used to define the side panels themselves. Although the closed tubes would provide adequate structural integrity, they too are available only in certain lengths and require butt welds or cutting to achieve the appropriate lengths. This again involves extra costs and waste. Moreover, closed box tubes are disadvantageous in that they cannot readily be inspected or protected from corrosion. Also, in order to keep their weight at an acceptable level, the metal thickness of the box tube sections must be kept relatively thin. This further degrades corrosion protection.
The sootblower frame in accordance with this invention is readily adapted for different lengths of sootblowers by using various lengths of flat sheet metal for the side panels of the frame. With the shorter sootblower lengths (up to approximately twenty-two feet) the sheet metal side panels can be used without further structural reinforcement. For intermediate lengths, angle iron is welded or bolted along the length of the side panels of the frame to increase its structural integrity and enable it to handle the loads associated with the longer length lance tube. The longest length devices, those generally greater than twenty-two feet in length, are further reinforced by adding an additional member to the side panels of the frame.
As mentioned previously, the requirements of joining separate lengths of stock material to form a sootblower frame of a desired length has its disadvantages. In accordance with this invention, a sootblower frame is provided in which the side panels can be formed from coiled sheet metal stock, available in substantially any length required. Since the side panels do not require forming of any type, with the exception of a flattening or straightening operation, length constraints are virtually eliminated and the side panels can be formed without seams thereby eliminating an inherent weakness of the prior designs.
In some sootblowers, a pair of laterally separated guide tracks or rails are provided to suspending the carriage as it moves between its advanced and retracted positions. Frequently, the lance tube is designed to be positioned off-center with respect to the two guide rails. This is known as handedness, left-handedness or right-handedness depending to which side of the lance tube is off-set.
Due to the significant fluid force of the blowing medium acting on the cross-section of the feed tube, substantial pressure forces also act on the carriage and the frame. When handedness is designed into the sootblower, significant imbalances in the forces applied are present. This leads to increased and uneven structural loading on both the frame and carriage. In one embodiment of the present invention, the sootblower features a balanced orientation with the lance tube being equidistantly positioned between the side tracks thus equalizing the loading of the frame.
In many sootblowers which are driven by a rotating pinion gear interacting with a toothed rack, difficulties are often presented in establishing the correct backlash or degree of intermeshing between the pinion gear and the rack. Improper backlash adjustment, with the backlash being too small, can lead to excessive loads on the various components and increased power consumption. Accelerated wear of the components occurs when the backlash is too great.
A sootblower in accordance with this invention incorporates a mechanism which readily permits the backlash of the pinion gear to be adjusted in the field. This mechanism utilizes an eccentric shaft to mount an upper carriage roller to the carriage. By changing the orientation of the eccentric shaft, and therefore the carriage roller with respect to the frame, the carriage can be raised or lowered with respect to the frame and the pinion gear adjusted relative to the rack.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiments and the appended claims, taken conjunction with the accompanying drawings.